Prevention of surface cracking due to formation of copper alloys of tin and antimony during reheating of steel

ABSTRACT

The surface cracking of steel containing copper and tin and/or antimony during reheating (surface hot shortness) due to the formation of alloys of copper, tin and/or antimony is prevented by adjusting the silicon and nickel content of the steel to an amount necessary to prevent the said alloy formation.

United States Patent [1 1 Copeland et al.

[ 1 PREVENTION OF SURFACE CRACKING DUE TO FORMATION OF COPPER ALLOYS OFTIN AND ANTIMONY DURING REHEATING OF STEEL [75] Inventors: Mark I.Copeland, Corvallis; John S.

Howe, Albany, both of Oreg.

[73] Assignee: The United States of America as represented by theSecretary of the Interior, Washington, DC.

[22] Filed: Dec. 5, 1974 [21] Appl. No.: 529,783

[52] US. Cl. 75/125; 72/365; 72/700 [51] Int. Cl. C22C 38/08; C22C 38/16[58] Field of Search 75/125, 129, 123 A; 148/2,

Cu- Sb ALLOY FORMED (SHADED AREA) OR NOT FORMED (UNSHADEDI HEATINGBOUNDARY SCHEDULE g BETWEEN PUSHER U o SOAKING A b E m 51 5.8- 0 mm 2 Lo I 0 v6 N o 6 z I o m U E 3 m I B D 0 5 I CI i o c B- I 5 o q o B I 0st I I o 4 Q I 2 oo o m 3 Ra 2m \nI l 1 0A my 0.2 0,4 05 05 L0 0.4

COPPER CONTENT WITH 003-005 Ni I WITH 0.08-0. NI

SILICON AND NICKEL CONTENTS NECESSARY TO PREVENT- CuSn ALLOY FORMATIONON STEELS CONTAINING COPPER AND TIN.

[451 Sept. so, 1975 [56] References Cited UNITED STATES PATENTS3,443,934 5/1969 Kubota et a1. 75/125 3,459,538 8/1969 Teramae et a175/125 Primary ExaminerL. Dewayne Rutledge Assistant E \'aminerArthur.I. Steiner Attorney, Agent, or FirmGersten Sadowsky; Donald R. Fraser57 ABSTRACT 7 Claims, 2 Drawing Figures Cu- Sb ALLOY FORMED (SHADEDAREA) OR 91 FQRMED ILJNHAQDI HEATING BOUNDRY CHEDULE e NQ BETWEEN PUSHERB O SOAKING A GA H I A\- 3 E 8 T I 1:: 9 E d 8 6 r I 0 0A m I o m z I o4 m E a A D I D i :7:

2 Em C M m m r1 o b o D N a 8 o n o D D o I o A u u D q 0' I 4 D U A 3 2\\\I I I d If! I I 042 0 4 0.6 0.8 ITO 0.4 0.6 0.8 L0

COPPER CONTENT WITH 0.04-006 NI WITH 0.09"O.l5 NI SILICON AND NICKELCONTENTS NECESSARY TO PFEVENT Cu-Sb ALLOY FORMATION ON STEELS CONTAININGCOPPER AND ANTIMONY,

US. Patent Sept. 30,1975 Sheet 1 of2 3,909,251

Cu- Sb ALLOY FORMED (SHADED AREA) OR NOT FORMED (UNSHADED) HEATINGBOUNDARY SCHEDULE Y E BETWEEN PUSHER I3 0 SOAKING A C. c I Q (I) E .8 oMOA o E \\A DJ 9 I... Q. (j Z I\ 8 .6-- I W Q 0 d3 I [I (j g FCYVL o k I3 05 I E1 0 m E 6 I K III I .2 0A GA I -I\ [10 U\ I U 0 v I D\ .8 I 5 II l .6 I I 0A E! (\1 k I\|-\ E] TL [1 A OA 1 v Q F4 2 D.\\ml\\\|\\\I\\\OA '\|:1'0\ ;\\I\\\\I\\\ COPPER CONTENT WITH 0,03-O .O5 Ni WITH0.08-O.II NI J SILICON AND NICKEL CONTENT-S NECESSARY TO PREVENT- Cu-SnALLOY FORMATION ON STEELS CONTAINING COPPER AND TIN.

US. Patent Sept. 30,1975 Sheet 2 Of 2 3,909,251

Cu- Sb ALLOY FORMED (SHADED AREA) OR NOT FORMED (UNSHADED) HEATINGBOUNDRY SCHEDULE Y E N 0 BETWEEN PUSHER U 0 SOAKING A I. A 0A n I- 8 w zn m 9 E (5 O 6 l Ii O 0A Qfi 8 O D E L z I O 4 L Q i I 2 D f D I: I A Uf 3 6 I .2 QRRR 'QVA A Q} PA PA *QQQQ M-fi 0 U D I l U I .c: .8 El E1 oD I a I o 5 2. 2 D g I E EI Q U 0 Q I I: III A L. E Q 2 \\\\|\\\\l\\\ (50.2 0.4 0.6 0.8 L0 0.4 0.6 0.8 I.

COPPER CONTENT WITH 0.04-0.06 Ni WITH 0.09- 0.|5 Ni FIG, 2 SILICON ANDNICKEL CONTENTs NECESSARY TO PREVENT Cu-Sb ALLOY FORMATION ON sTEELsCONTAINING COPPER AND ANTIMONY.

PREVENTION OF SURFACE CRACKING DUE TO FORMATION OF COPPER ALLOYS OF TINAND ANTIMONY DURING REHEATING OF STEEL BACKGROUND OF THE INVENTION ll.Field of the Invention This invention relates to steel metallurgy andmore particularly to preventing the formation of copper alloys of tinand/or antimony on the surface of steel containing these elements onreheating.

2. Description of the Prior Art During reheating, several methods areavailable for preventing copper from forming on the surface of steelcontaining this element. However, no methods are available, so far as isknown, for preventing copper alloys of tin and/or antimony fromformingon the surface of steel containing these elements during areheating operation. The thus formed copper or copper alloy aredetrimental because they penetrate the steel austentite grain boundariesduring hot rolling. These penetrations weaken the steel surface andcause the formation of deep cracks, especially in the presence oftensile stresses such as occur during hot rolling operations. The alloysmake the steel more subject to surface hot shortness (cracking) duringhot working than copper alone.

SUMMARY or THE INVENTION This invention provides a method for preventingthe formation of these detrimental alloys during the reheating of steelcontaining copper, tin and/or antimony by incorporating nickel andsilicon in the steel composition. We have discovered that thepresence ofnickel and silicon prevents the formation of said alloys on the surfaceof the steel.

Normally when a steel containing copper, tin, antimony and nickel isreheated in an oxidizing atmosphere, in accord with the-usual practice,these elements concentrate at the steel surface. Copper alloys of tin orantimony, or both, form on the surface when the copper present exceedssolubility of copper in iron. In the presence of copper, tin andantimony are more detrimental than copper alone as they lower thesolubility of copper in iron and thus promote the formation of greateramounts of copper alloy on the steel surface.

In contrast to antimony and tin, nickel has been found to slightlyincrease the solubility of copper in iron. Silicon results in theformation of fayalite(Fe .steel containing copper, tin and antimonyresulted in a marked inhibiting effect on the production of copperalloys of tin and antimony on the surfaceduring reheating.Parenthetically, in the compositions recited, all,

percentages in the specification and claims are by weight.

OBJECTS OF THE INVENTION It is an object of this invention to preventthe formation of copper alloys of tin and/or antimony on the sur' faceof steel containing these elements during reheating.

nickel content of the steel composition.

. i a It is a further object of this invention to prevent the formationof such alloys by adjusting the silicon and.

It is a further'object of this invention to prevent the formationofcopper alloys of tin and/or antimony on the surface of asteelcontaining these elements during a reheating by incorporating in saidsteel silicon and nickel, the amounts of the above elements other thanFe, C and Mn being: Cu, up to 1%, Si, up to 1.0%,Sb, up to 0.20%; Sn, upto 0.31%; and Ni, from'0.03 to 0.15%.

It is a further object of this invention to use less desirable grades ofscrap iron and steel containing copper and tin or antimony by adjustingthe molten scrap composition to include percentages of nickel andsilicon, operative to prevent copper, tin and/or antimony alloyformation during reheating, and forming into a shape, and subjecting itto reheating.

It is a further object to conduct the heat treatment in an oxidizingatmosphere in a hot combustion gas containing about 2% by voluume ofoxygen at temperatures of from about 1250C. to about 1300C.

It is a further object to conduct the reheating in anoxidizing gasshowing a movement ofat least one foot per second through the heatingzone.

Further objects will become apparent from the following description ofthe invention and from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are graphs showing thesilicon and nickel content necessary to prevent the copper-tin andcopper-antimony alloy formation, respectively, on steels.

BRIEF DESCRIPTION OFPREFERRED EMBODIMENTS It was found that thebeneficial properties. of molten fayalite (Fe SiO formed from thesilicon present in the steel was due to its penetration through thescale grain boundaries to the scale surface. Establishment of t localiron-fayalite-oxygen electrolyte cells in the scale promoted theformation of iron-rich iron-copper alloys instead of copper-rich,copperiron alloys. Since an oxygen potential at the scale surface isrequired, the free excess oxygen content of the reheating furnace mustbe regulated to assure a sufficient concentration. It was found that anexcess free oxygen content of 2 vol. percent of a burning natural gascombustion atmosphere was generally satisfactory, Liquid petroleumproducts or other hydrocarbon materials may be substituted for naturalgas, if desired. A uniform heating rate was foundto be desirable.

Thebeneficial properties of fayalite in preventing the formation ofcopper on the surface of steel was foundto extend to the preventionofthe formation of copper alloys of tin or antimony as well. The followingexamples show the effects of this presence of Si and Ni in preventingthe formation of copper alloys of tin or antimony.

EXAMPLE 1 The reheating was carried out in two types of furnaces. Onewas a pusher (continuous-type furnace having a 2 hour reheating scheduleof from 375 i 20C. to l310 i C. This is represented in the graphs ofFIGS. 1 and 2 by solid lines.'The other type was a soaking pit furnacehaving a 8 hour schedule from 820 i to 1'310 10C. This is represented bya dotted line.

The formation or lack of formation of copper-tin and copper-antimonyalloys was noted at various alloy compositions and the results aretabulated in the graphs of FIGS. 1 and 2 (lefthand column). Alloyformaton occurs in the cross-hatched regions. It is apparent that forsteels containing 0.03 to0.06% Ni that the larger the copper and tin orantimony content of the steel, the greater the amount of siliconnecessary to prevent copper alloy formation. Copper alloys were notprevented from forming on steels containing 0.12 to 0.16% Sn and morethan about 0.7 Cu or steels with 0.24 'O.3 1% Sn and more than about 0.5Cu. For the antimony steels, copper alloys were not prevented by up to1% Si from forming on steels containing 0.14 to 0.20% Sb at any coppercontent.

EXAMPLE 2 The nickel content of the steels was increased to 0.08

to 0.15% and the heating tests of Example 1 were repeated. Larger nickelcontents were investigated as copper alloy formation could not beprevented in Example l by 0.03 to 0.06% Ni and up to 1% Si on many steelcompositions containing up to 1% Cu. The amount of silicon required toprevent copper-tin or copper-antimony formation with the higher nickelcontent is given in the righthand columns of FIGS. 1 and 2,respectively. By comparing the left and righthand columns of theFigures, it is apparent that much less silicon is necessary to preventcopper alloy formation on steels containing 0.09 to 0.15% Ni than onthose containing 0.03 0.06% Ni. Moreover, the amount'of silicon requiredto prevent copper alloy formation on steels containing 0.4% or lesscopper content and 0.12

- 0.16% Sn or 0.07 O. 10% Sb is similar to the amount used in manycommercial steels, 0.2 to 0.4 Si.

Steels containing larger nickel contents, up to 0.50%, were likewiseinvestigated. The results with such higher nickel content steels were nobetter generally than with steels containing 0.08 to 0.11% Ni.

When both tin and antimony are present in a steel with 0.08 0.15% Ni,the combined total percent of tin and antimony generally should notexceed 0.10% for steel containing up to 1% Cu. The combined total shouldnot exceed 0.20% for steels with up to 0.5% Cu. Reheating of steelscontaining copper contents greater than 0.5% Cu and tin and antimonycombined contents greater than 0.20% generally should not be consideredunless formation of copper alloys is desired.

Without wishing to be bound by any theory, one possible explanation forthe beneficial effects of the combination of silicon and nickel inpromoting the formation of iron-rich iron-copper alloys instead ofcoppertin or -antirnony alloys on the surface of steels containingcopper as well as tin or antimony is the following: Iron-rich alloyshave been found to'form on steel surfaces only when the steel was heatedabovc 1205C., which is common in rolling operations. At thesetemperatures, fayalite melts and' penetrates the grain boundaries of thesteel. The higher the silicon content,

the greater the'amount of fayalite produced and concomrnitantly, thegreater penetration of larger amounts fayalite to the scale surface.Under these conditions, iron alloy-fayalite-oxygen electrolytic cellsare established in the scale. The iron oxides of the scale and themolten fayalite act as electronic and ionic conductors, respectively.Oxygen ions are transported by the molten fayalite to the steel surfaceand Fe, Cu, Sn, Sb and Ni ions migrate to the scale surface. The localcell action promotes the formation of iron-rich copper alloys at thesteel surface. When Sn or Sb are present in addition to copper, aminimum nickel content of 0.03% is necessary, with from about 0.08 to0.15% as generally desirable. The nickel, which concentrates at thesteel surface as the steel scales, increases the solubility of copper atthe steel surface and regulates the copper composition of the steelsurface to below its solubility in iron.

The process has been described for reducing surface hot shortness ofcopper steels containing tin or antimony by the addition of silicon andnickel generally and by examples with reference to specificcompositions. It will be apparent to those skilled in the art thatvarious modifications of the process and the compositions disclosed maybe made without departing from the spirit of the invention.

What is claimed is:

1. In a method of producing steel having resistance to hot shortness dueto the formation of copper-tin and copper-antimony alloys on the steelsurface during reheating, said steel containing copper in an amount upto about 1% by weight and a member of the group consisting of tin andantimony, and mixtures thereof, tin and antimony being present inamounts of up to about 0.31% and up to about 0.20% respectively, andwhen both are present, the total not exceeding about 0.10% for steelscontaining up to 1% Cu and not exceeding 0.20% for steels containing upto 0.5% Cu, which method includes melting and solidification, theimprovement comprising:

in the melting step, adjusting the content of silicon and nickel in thesteel to from about 0.2% to about 1.0% for the silicon, and from about0.03% to about 0.15% for the nickel, said ranges selected falling withinthe unshaded portions of the graphs of FIGS. 1 and 2.

2. The method of claim 1 wherein the steel contains tin in an amount ofup to about 0.31%, the silicon content is from about 0.2% to about 1.0%,the nickel content ranges from about 0.03 to about 0.05%, the coppercontent ranges from about 0.2 to about 1.0%, and the amount of siliconand copper falls within the unshaded portion of the lefthand column ofFIG. 1.

3. The method of claim 1 wherein the steel contain tin in an amount ofup to 0.31%, the silicon content is from about 0.2% to about 1.0%, thenickel content ranges from about 0.08 to about 0.11%, the copper contentranges from about 0.2% to about 1.0%, and the amount of silicon andcopper falls within the unshaded portion of the righthand column of FIG.1.

4. The method of claim 1 wherein the steel contains antimony in anamount of up to 0.20%, the silicon content is from about 0.2% to about1.0%, the copper content is from about 0.2% to about 1.0%, the nickelcontent is from about 0.04 to about 0.06% and the amounts of silicon andcopper falls within the unshaded portion of the lefthand column of FIG.2.

5. The method of claim 1 wherein the steel contains antimony in anamount of up to 0.20%, the silicon content is from about 0.2% to about1.0%, the copper content is from about 0.2% to about 0.1%, the nickelcontent is from about 0.9% to about 0.15%, and the amount of silicon andcopper falls within the unshaded portion of the righthand column of FIG.2.

6. In a method of producing an upgraded steel having reduced surface hotshortness from scrap steel pieces containing in the aggregate copper anda member of the group consisting of tin and antimony and mixturesthereof, which comprises selecting portions of steel scrap to give anoverall steel composition containing in addition to Fe, C and Mn up toabout 1% copper, up to about 0.31% tin, up to about 0.20% antimony, butwhen both tin and antimony are present the combined total percentage ofthese elements is no more than about 0.10% for steels containing up to1% Cu and not exceeding 0.20% for steels containing up to 0.5% Cu, theimprovement comprising;

melting the selected steel scrap; adjusting the nickel content to fromabout 0.03% to about 0.15% and adjusting the silicon content from about0.2% to about 1.0%;

the ranges selected falling within the unshaded portions of the graphsof FIGS. 1 and 2.

7. The method of claim 6 wherein the nickel content is adjusted to fromabout 0.08 to about 0.15% and the ranges selected fall within theunshaded portions of the righthand columns of FIGS. 1 and 2.

1. IN A METHOD OF PRODUCING STEEL HAVING RESISTANCE TO HOT SHORTNESS DUETO THE FORMATION OF COPPER-TIN AND COOPERANITOMY ALLOYS ON THE STEELSURFACE DURING REHEATING, SAID STEEL CONTAINING COOPER IN AN AMOUNT UPTO ABOUT 1% BY WEIGHT AND A MEMBER OF THE GROUP CONSISTING OF TIN ANDANTIMONY, AND MIXTURES THEREOF, TIN AND ANITOMY BEING PRESENT IN AMOUNTSOF UP TO ABOUT 0.31% AND UP TO ABOUT 0.20% RESPECTIVELY, AND WHEN BOTHARE PRESENT, THE TOTAL NOT EXCEEDING ABOUT 0.10% FOR STEELS CONTAININGUP TO 1% CU AND NOT EXCEEDING 0.20% FOR STEELS CONTAINING UP TO 0.5% CU,WHICH METHOD INCLUDES MELTING AND SOLIDIFICATION, THE IMPROVEMENTCOMPRISING: IN THE MELTING STEP, ADJUSTING THE CONTANT OF SILICON ANDNICKEL IN THE STEEL TO FORM ABOUT 0.2% TO ABOUT 1.0% FOR THE SILICON,AND FROM ABOUT 0.03% TO ABOUT 0.15% FOR THE
 2. The method of claim 1wherein the steel contains tin in an amount of up to about 0.31%, thesilicon content is from about 0.2% to about 1.0%, the nickel contentranges from about 0.03 to about 0.05%, the copper content ranges fromabout 0.2 to about 1.0%, and the amount of silicon and copper fallswithin the unshaded portion of the lefthand column of FIG.
 1. 3. Themethod of claim 1 wherein the steel contain tin in an amount of up to0.31%, the silicon content is from about 0.2% to about 1.0%, the nickelcontent ranges from about 0.08 to about 0.11%, the copper content rangesfrom about 0.2% to about 1.0%, and the amount of silicon and copperfalls within the unshaded portion of the righthand column of FIG.
 1. 4.The method of claim 1 wherein the steel contains antimony in an amountof up to 0.20%, the silicon content is from about 0.2% to about 1.0%,the copper content is from about 0.2% to about 1.0%, the nickel contentis from about 0.04 to about 0.06% and the amounts of silicon and copperfalls within the unshaded portion of the lefthand column of FIG.
 2. 5.The method of claim 1 wherein the steel contains antimony in an amountof up to 0.20%, the silicon content is from about 0.2% to about 1.0%,the copper content is from about 0.2% to about 0.1%, the nickel contentis from about 0.9% to about 0.15%, and the amount of silicon and copperfalls within the unshaded portion of the righthand column of FIG.
 2. 6.In a method of producing an upgraded steel having reduced surface hotshortness from scrap steel pieces containing in the aggregate copper anda member of the group consisting of tin and antimony and mixturesthereof, which comprises selecting portions of steel scrap to give anoverall steel composition containing in addition to Fe, C and Mn up toabout 1% copper, up to about 0.31% tin, up to about 0.20% antimony, butwhen both tin and antimony are present the combined total percentage ofthese elements is no more than about 0.10% for steels containing up to1% Cu and not exceeding 0.20% for steels containing up to 0.5% Cu, theimprovement comprising; melting the selected steel scrap; adjusting thenickel content to from about 0.03% to about 0.15% and adjusting thesilicon content from about 0.2% to about 1.0%; the ranges selectedfalling within tHe unshaded portions of the graphs of FIGS. 1 and
 2. 7.The method of claim 6 wherein the nickel content is adjusted to fromabout 0.08 to about 0.15% and the ranges selected fall within theunshaded portions of the righthand columns of FIGS. 1 and 2.